The present invention relates to a cylindrical battery having a spirally wound electrode group formed by spirally winding a positive electrode plate, a negative electrode plate, and a separator interposed between the two electrodes, and more particularly to an improvement in the connecting portion between an electrode lead of the electrode group and a bottom surface of a battery case.
Alkaline storage batteries, such as nickel-cadmium storage batteries and nickel-metal hydride storage batteries, and primary and secondary lithium batteries are typical examples of the cylindrical battery having an electrode group formed by spirally winding a positive electrode plate, a negative electrode plate, and a separator interposed between the two electrodes. In this type of cylindrical battery, the cylindrical metallic battery case housing the electrode group also serves as the terminal of one electrode, and the lead plate of the one electrode in the electrode group, for example, the negative electrode, is connected to the inner bottom surface of the battery case.
In cylindrical batteries having such construction, there is a possibility that an end of the other electrode in the electrode group, for example, the positive electrode, may touch the inner bottom surface of the battery case or the lead plate connected thereto, causing internal short-circuiting.
To address this problem, the prior art discloses a construction aimed at preventing internal short-circuiting by providing an annular insulating plate between the bottom of the electrode group and the lead plate drawn from the electrode group.
In this construction, however, the insulating plate is only inserted between the electrode group and the bent lead plate. As a result, a situation can occur where the insulating plate will be displaced, for example, during insertion of the electrode group with the insulating plate assembled thereon into the battery case. This gives rise to the danger of internal short-circuiting, defeating its intended purpose of insulation.
Furthermore, since no means are provided for positioning the insulating plate in place, the prior art construction involves a possibility that if the center hole of the insulating plate is not positioned above the upper portion of the lead plate, a difficulty may arise when connecting the lead plate to the inner bottom surface of the battery by, for example, resistance welding or the like.